Method of making a poly(L-lactide) stent with tunable degradation rate

Abstract

Methods of treating with a biodegradable polymeric stent made from poly(L-lactide) and a low concentration of L-lactide monomer is disclosed. The concentration of L-lactide is adjusted to provide a degradation behavior that is suitable for different treatment applications including coronary, peripheral, and nasal.

What is claimed is: 
     
       1. A method of making a stent for treating a diseased section of a blood vessel, comprising:
 extruding a polymer composition comprising poly(L-lactide) to form a tube; 
 processing the extruded tube to increase crystallinity of the tube to between 20-50%; and 
 laser cutting the processed tube to form a stent comprising a scaffolding, wherein the scaffolding comprises greater than 95 wt % poly(L-lactide) and between 0.05 to 0.5 wt % L-lactide monomer mixed, dispersed, or dissolved within the poly(L-lactide). 
 
     
     
       2. The method of  claim 1 , wherein the processing comprises heating and radially expanding the extruded tube to induce orientation in the polymer. 
     
     
       3. The method of  claim 2 , wherein the extruded tube is radially expanded to a degree of radial expansion of between 200-500%. 
     
     
       4. The method of  claim 2 , wherein the extruded tube is heated to a temperature between 70° C. and 95° C. prior to expansion. 
     
     
       5. The method of  claim 1 , wherein the scaffolding is composed of a pattern of struts, the pattern including a plurality of cylindrical rings connected by linking struts. 
     
     
       6. The method of  claim 5 , wherein the struts have a rectangular cross-section, the cross-sectional area being between 20,000 and 25,000 μm 2 . 
     
     
       7. The method of  claim 1 , wherein the number average molecular weight of the poly(L-lactide) of the scaffolding is between 60,000 and 300,000, relative to polystyrene standards. 
     
     
       8. The method of  claim 1 , further comprising mixing the L-lactide monomer with the poly(L-lactide). 
     
     
       9. The method of  claim 8 , wherein the mixing comprises mechanically blending the L-lactide monomer with the poly(L-lactide). 
     
     
       10. The method of  claim 8 , wherein the L-lactide monomer is mixed with the poly(L-lactide) using solvent blending. 
     
     
       11. The method of  claim 10 , wherein the solvent blending comprises:
 making a master batch of the poly(L-lactide) and the L-lactide monomer having a concentration of the L-lactide monomer larger than a target concentration, wherein the master batch is made by dissolving the L-lactide monomer and the poly(L-lactide) in a solvent and evaporating the solvent to form the master batch which is a mixture of the poly(L-lactide) and the L-lactide monomer; and 
 making the polymer composition by mixing the master batch with an amount of the poly(L-lactide) that is sufficient to obtain the target L-lactide monomer concentration in the polymer composition. 
 
     
     
       12. The method of  claim 1 , further comprising:
 preparing a solution of the L-lactide monomer dissolved in a solvent; 
 spraying the solution on pellets of the poly(L-lactide); 
 removing the solvent to leave the L-lactide monomer deposited on the pellets; and 
 using the polymer with the deposited L-lactide monomer as the polymer composition for the extruding step.